1. Field of the Invention
The present invention relates to an energy-trap chip-type piezoelectric resonance component including an improved piezoelectric resonance element and a holding structure therefor.
2. Description of the Background Art
FIG. 1 is a perspective view showing an example of a conventional energy-trap piezoelectric resonance element 1. This piezoelectric resonance element 1 is formed by a rectangular piezoelectric plate 2 which is polarized along arrow P. First and second resonance electrodes 3 and 4 are formed on both major surfaces of the piezoelectric plate 2, to be opposed to each other on a central region of the piezoelectric plate 2. The first resonance electrode 3 extends from the central region to an end of the piezoelectric plate 2 on its upper surface. On the other hand, the second resonance electrode 4 extends from the central region to another end of the piezoelectric plate 2 on its lower surface.
In the piezoelectric resonance element 1, overlapping portions of the first and second resonance electrodes 3 and 4 define an energy-trap resonance part. When an ac voltage is applied across the first and second resonance electrodes 3 and 4, the resonance part is excited in a shear mode so that vibrational energy is trapped therein.
As a chip-type electronic component employing the aforementioned piezoelectric resonance element 1, FIG. 2 shows a known structure which is obtained by bonding protective substrates 5 and 6 on upper and lower portions of the piezoelectric resonance element 1 with adhesives. The protective substrates 5 and 6 have substantially U-shaped side elevational, shapes respectively, to provide spaces for allowing vibration of the resonance part within the cavities 5a and 6a.
In the structure shown in FIG. 2, it is necessary to prepare the protective substrates 5 and 6 having the cavities 5a and 6a, in order to provide the spaces for allowing vibration of the vibrating part of the piezoelectric resonance element 1. Namely, it is necessary to prepare not flat plate type protective substrates but the protective substrates 5 and 6 which are provided with the cavities 5a and 6a. Thus, the cost for the protective substrates 5 and 6 is increased, and working such as molding is complicated.
On the other hand, it is conceivable to apply adhesives onto upper and lower portions of the piezoelectric resonance element 1 in thicknesses allowing vibration of the vibrating part, for bonding flat plate type protective substrates thereto.
However, it is extremely difficult to reliably define spaces for allowing vibration of the resonance part by adhesives. In order to apply adhesives to the upper and lower surfaces of the piezoelectric resonance element 1 except the vibrating part for bonding the flat plate type protective substrates, for example, it is necessary to apply a certain degree of pressure. Due to this pressure, however, the adhesives may flow out toward the resonance part or onto side surfaces, to excessively reduce the thicknesses of the adhesive layers.
There has also been developed a method of employing double-fluid epoxy adhesives or the like and temporarily hardening the same for ensuring thicknesses of adhesive layers, for thereafter bonding flat plate type protective substrates. In this case, however, a long time is required for the adhesion since it is necessary to temporarily harden the adhesives, while it is extremely difficult to control the thicknesses of the adhesive layers with this method.